The present invention relates to a pneumatic vehicle tire, and more specifically to a pneumatic vehicle tire afforded runflat capability by means of a support structure within the tire cavity.
It is desirable for a tire tread to bear against the ground uniformly along its width, so that the load on the tire is evenly distributed. When a tire is under-inflated, and especially deflated, the portion of the tire""s sidewalls near the ground bulge outward. If the tire is stiff along the sidewalls, tread and shoulders, the sidewall bulge causes the lateral-center of the footprint (portion of the tread contacting the ground) to lift off the ground, forming an upward bow in the lateral cross-section of the footprint. The stiff tire acts like a lever, and the shoulder against the ground acts as its fulcrum. This xe2x80x9clateral tread-liftxe2x80x9d is aggravated by sidewalls and tread that are relatively stiff or thick, and by a small ply line radius (i.e. sharp bend) in the shoulder.
Similarly, when the tire is under-inflated, and especially deflated, the circumferential cross-section of the tread is sharply bent at the front and rear edges of the footprint, causing the circumferential-center of the footprint to lift off the ground, forming an upward bow in the circumferential cross-section of the footprint. The stiff tread acts like a lever in 2 places, and the front and rear edges of the footprint shoulder against the ground act as two fulcrums. This xe2x80x9ccircumferential tread-liftxe2x80x9d is aggravated by a tread that is relatively stiff or thick.
Tread-lift, whether lateral or circumferential, causes the center portion of the tread to bear little or none of the tire""s load, which produces several problems. It degrades vehicle handling characteristics, especially in cornering. It increases tread wear near the shoulders and increases material fatigue under the tread due to the cycling of the bending stresses, and hence shortens tire life. Tread-lift is a problem whether the tread center actually lifts off the ground or merely loses pressure against the ground.
When a tire is under-inflated, its tread loses lateral stability and is prone to move (sway) laterally at the footprint. This yields a swerving ride and poor handling.
Pneumatic tires designed for continued operation under deflated or under-inflated conditions are referred to as xe2x80x9crunflatxe2x80x9d tires, as they are capable of being driven in the flat condition, without the sidewalls collapsing or buckle while driving to where the tire can be changed. In general, xe2x80x9crunflatxe2x80x9d means that the tire structure alone has sufficient strength to support the vehicle load when the tire is operated in the deflated state.
Generally, runflat tires incorporate, within the sidewalls, reinforcements called xe2x80x9cwedge insertsxe2x80x9d or xe2x80x9csidewall insertsxe2x80x9d, which are fillers generally having a cross-sectional crescent shape, that are sufficiently rigid to keep the sidewalls from collapsing or buckling. Such sidewalls are thicker and stiffer than in non-runflat tires, so that the tire""s load can be carried by a deflated tire without compromising vehicle handling until the tire can be repaired or replaced. Such inserts are located in the inner surface of the sidewall portion of the carcass, which is the region in the tire experiencing the greatest flex under load. In such runflat designs, the entire sidewall has an approximately uniform thickness corresponding to the thickness of the bead region, so as to provide runflat supporting rigidity.
Runflat tires using sidewall inserts suffer from several problems: In runflat mode (i.e. while running under-inflated), due to the large mass of rubber required to reinforce the sidewalls, heat and material fatigue from cyclical flexure of the sidewalls is a major cause of tire failure. In runflat mode, the thicker, stiffer sidewalls of runflat tires renders them more prone to lateral tread-lift, with all the aforementioned problems associated with tread-lift. Also, runflat tires suffer from lateral tread-sway when under-inflated, as do all tires.
Even during normal inflated operation, the hysteresis of the material of the thickened runflat tire""s sidewalls contributes to its rolling resistance and fatigue, which reduces the vehicle""s fuel efficiency and tire life. Also, during normal inflated operation, the increased sidewall stiffness in runflat tires produces a rougher (less soft, less comfortable) ride and worse handling characteristics. Also, the additional weight of a sidewall insert renders it difficult to handle and mount. Moreover, the additional sidewall inserts add cost to the manufacturing process.
U.S. Pat. No. 5,368,082, to Oare et al, having a common assignee with the present invention, disclosed the first commercially accepted runflat pneumatic radial ply tire, employing sidewall inserts to improve stiffness. This runflat tire required about six additional pounds of weight per tire to support an 800 lb. load when deflated. This weight penalty was even greater for heavier vehicles with high aspect ratios, such as luxury sedans. U.S. Pat. Nos. 5,427,166 and 5,511,599, both to Willard, incorporate an additional third ply and third insert in each sidewall to further increase runflat performance. The resulting improvement in runflat ability comes at the price of further increased weight, flexural heat, material fatigue, tread-lift and manufacturing cost, and poorer handling and rougher ride.
Another method to achieve runflat ability is by incorporating a support structure within the tire cavity which does not contact the tread during normal inflated operation, but supports the tread and keeps it from collapsing when the tire is deflated. Advantages of using these support structures over using sidewall inserts is that they do not degrade tire performance during normal inflated operation, they can be implemented with standard (non-runflat) tires, do not increase tire manufacturing cost, and can prevent tread-lift. Some examples of these support structures are as follows:
U.S. Pat. No. 4,257,467 discloses, in a second embodiment shown in FIG. 3, a toroidal support element including a torus-like body of circular cross section whose xe2x80x9cresilience can be increased by recesses or bore 30 running substantially parallel to the axis of the body 29xe2x80x9d. This does not prevent lateral tread-sway.
U.S. Pat. No. 5,271,444 discloses a rubber solid inner tire 30 fixedly mounted to the inner surface of the tread. This does not prevent lateral tread-sway and adds significant weight.
U.S. Pat. Nos. 4,254,810 and 3,993,114 disclose designs, employing an inner tube disposed within the tire cavity, that indirectly supports the tread during runflat mode but not during normal inflated operation. These designs do not stiffly support the tread nor prevent tread-lift or lateral tread-sway during runflat mode. They require two valves or equivalent.
U.S. Pat. Nos. 3,857,427; 4,346,747; 4,157,106 and 4,193,436 disclose various other annular support members surrounding the rim, that support the tread during runflat mode, but are spaced from the tread during normal inflated operation. These, too, do not prevent lateral tread-sway and add significant weight.
It is an aspect of the present invention to provide a tire as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary aspects.
It is an aspect of the present invention to provide runflat ability to a non-runflat tire, with a support structure that is relatively light, reduces tread-lift and lateral tread-sway, and does not degrade handling in normal-inflated operation.
Additionally, it is an aspect of the present invention to increase the runflat performance of a runflat tire, with a support structure that is relatively light, reduces tread-lift and lateral tread-sway, and does not degrade handling in normal-inflated operation.
Additionally, it is an aspect of the present invention to maintain a tight seal between the bead and rim during under-inflated operation.
A tire assembly having runflat capability comprises a tire mounted to a rim to provide a tire cavity that is defined by a carcass circumferential inner surface, two sidewall inner surfaces and the rim. The tire assembly is characterized by a circumferential platform disposed within the tire cavity, around the rim, having a circumferential radially-outer surface (xe2x80x9cplatform surfacexe2x80x9d) and two platform sides. The tire assembly also has one or more hollow deformable hoops within the tire cavity, disposed around the platform surface, between the platform and the carcass circumferential inner surface, so that under normal inflation the one or more hoops do not contact either the carcass circumferential inner surface or the sidewall inner surfaces, but below a first runflat inflation pressure, the one or more hoops contact and support the carcass circumferential inner surface. Below a second runflat inflation pressure, lower than the first runflat inflation pressure, the hoops bulge laterally and press against the sidewall inner surfaces to support the sidewalls and prevent them from buckling.
The one or more hoops are constructed of a material selected from the group including plastic, rubber based material, and spring metal.
The one or more hoops have reinforced walls that are reinforced by means including corrugated walls, cord reinforcements, and/or fiber reinforcements. The number of hoops is three or more and preferably an odd number.
The hoops have cross-sectional shapes chosen from round or elliptical, wherein the major axis of each elliptical hoop is preferably aligned radially (but may be aligned axially or in any direction depending on the specific tire design), and where the major axes of all elliptical hoops and the diameters of all round hoops are preferably equal. The cross-sectional elliptical shapes of all the hoops can all be the same, or different but symmetric around an equatorial plane (EP) of the tire assembly.
In one embodiment, the platform surface is rigid and meridionally flat.
In another embodiment, the platform surface is flexible and bowed, and below the second runflat inflation pressure, the platform surface is straightened, and presses against the tire""s inner bead surfaces to lock the tire""s beads more tightly in place.
One or more of the hoops can be slidably affixed to the platform by means such as having each of the one or more of the hoops having at least one xe2x80x9cTxe2x80x9d-shaped key in the hoop""s inner periphery slidably attached into a corresponding inverted xe2x80x9cTxe2x80x9d-shaped cavity within the platform.
Also the hoops can be affixed together at their mutual peripheries of contact.